1. Field of the Invention
The present invention relates to a single-mode optical fiber usable as a transmission line in optical communications and the like; and, in particular, to a dispersion-shifted optical fiber suitable for wavelength division multiplexing (WDM) transmission.
2. Related Background Art
In general, a WDM transmission system using optical fiber networks is a system enabling long-distance, large-capacity optical data communications, and is constituted by a transmitter/receiver for transmitting and receiving WDM signals of a plurality of wavelengths (light signals), an optical amplifier such as an optical fiber amplifier for amplifying the WDM signals, an optical fiber which is a transmission medium, and the like. In such a WDM transmission system, the wavelength band that can optically be amplified in the optical amplifier is from 1530 nm to 1560 nm, whereas the low-loss wavelength band in the optical fiber is from 1400 nm to 1700 nm. As a consequence, the wavelength band utilizable as the WDM signals in the conventional WDM transmission system has substantially been limited to a width of about 30 nm from 1530 nm to 1560 nm.
The amplification of WDM signals by the optical amplifier increases the optical power of each light signal in the optical fiber acting as the transmission medium, thereby causing nonlinear phenomena such as four-wave mixing, self phasemodulation, modulation instability, and the like. In particular, the four-wave mixing causes power variations among the individual signal components, whereas the self phase modulation distorts the pulse waveform of each light signal upon an interaction with the chromatic aberration of the optical fiber (hereinafter referred to as dispersion), whereby the occurrence of such nonlinear phenomena limits the normal transmission of light signal.